Various kinds of microscopes are utilized for magnified observation of an eye in the field of ophthalmology. Examples of such ophthalmological microscopes include slit lamp microscopes and surgical microscopes. There are ophthalmological microscopes that include an image sensor for imaging an eye, and those that include a binocular optical system that provides binocular disparity for stereoscopic observation.
The ophthalmological microscopes may be used in combination with another ophthalmological apparatus. For example, as disclosed in U.S. Pat. No. 8,049,873 (Patent Document 1), a system is known in which an optical coherence tomography (OCT, hereinafter) apparatus is combined with an ophthalmological microscope. The OCT apparatus is utilized for, for example, acquiring cross sectional images, acquiring three dimensional images of an eye, measuring the sizes of ocular tissues (e.g., the thickness of the retina), and acquiring functional information on an eye (e.g., the blood flow information).
[Patent Document 1] U.S. Pat. No. 8,049,873
To ophthalmic instruments that project light toward or into eyes, a standard that prescribes requirements concerning the safety of light radiation is applied. Such standards include standards concerning protection of eyes from light hazards and the like. Protection of the eye from light hazards is prescribed in, for example, International Organization for Standardization (ISO) 15004-2: 2007 (Ophthalmic instruments—Fundamental requirements and test methods—Part 2: light hazard protection) (JIST 15004-2: 2013).
However, in the system in which an OCT apparatus is combined with an ophthalmological microscope, for example, there are cases in which illumination light from the ophthalmological microscope and measurement light from the OCT apparatus are simultaneously projected onto the subject's eye in order to acquire OCT images during surgery. In the case of projecting both the illumination light and the measurement light onto the subject's eye while satisfying the aforementioned standards, there are cases in which the amount of the illumination light or the amount of the measurement light to be projected onto the subject's eye becomes insufficient. If the amount of the illumination light or the amount of the measurement light are insufficient, the image quality of an observation image based on the returning light of the illumination light or the image quality of an OCT image deteriorates. To deal with this problem, if the amount of the illumination light or the amount of the measurement light is increased, the aforementioned standards cannot be satisfied and there is a danger of harmful influence on the subject. As described thus far, there is a trade-off relationship between the safety of the subject's eye and the improvement of the image quality. This brings upon a problem of difficulty in satisfying both the safety of the subject's eye and the improvement of the image quality.